1. Technical Field of the Invention
This invention relates to telecommunication systems and, more particularly, to a system and method of reallocating satellite gateways when a gateway or satellite radio link becomes inoperative in a radio telecommunications network.
2. Description of Related Art
In some areas of the world, transmissions to and from mobile stations are routed through communication satellites. The satellites are typically distributed either in geosynchronous orbit or mid-earth orbit. When in geosynchronous orbit, a single geosynchronous satellite (such as Thuraya, EAST, APMT, etc.) provides radio access between the radio telecommunications network and its mobile stations (MSs). When satellites are placed in mid-earth orbit, a constellation of satellites is required in order to provide continuous coverage of the service area of the telecommunications network since individual satellites move into and out of the service area.
Communications between satellites and the radio telecommunications network are routed through satellite gateways. Each gateway is responsible for providing telecommunications services to mobile stations in a particular geographic region. Two types of failures can occur which adversely impact the delivery of telecommunications services. The first type of failure is a ground failure which involves the loss of a gateway which communicates with one or more satellites. The loss of a gateway causes a loss of telephone service to all of the MSs in the service area of the failed gateway. Radio telecommunications services to the rest of the network may not be affected since the satellites and other gateways are still operational.
A second type of failure is experienced when a satellite becomes either completely disabled, or partially disabled. Alternatively, the link between the gateway and the satellite may be degraded for a number of reasons such as a misalignment or pointing error in the satellite antennas pointing at the ground, attenuation of the signal due to weather or atmospheric conditions, or misalignment of the satellite's solar arrays which cause loss of power. The effects of this type of failure vary since MS terminating traffic into the gateway may be more than can be handled by the available radio resources. For example, there may not be sufficient bandwidth or power on the link to perform paging, obtain page responses, and set up traffic channels. Since the gateway is still operational, but the satellite is not, the gateway attempts to set up the call in the normal manner through the satellite. The gateway sends out paging messages, but the MS is never paged by the satellite, and the call fails. When the paging timer times out, the call may be forwarded to voice mail. Unfortunately, this takes a long time, and there is a high rate of call abandonment as a result.
If the satellite is completely disabled, and the satellite is in a geosynchronous orbit, then effectively all radio access is lost for the network users. If the satellite is completely disabled, and the satellite is in a mid-earth orbit, then services may be lost or degraded whenever the failed satellite is over the network's service area. If the satellite is partially disabled, or experiences a mispointing error, the problem may affect the quality of the radio interface, while not preventing communications entirely. In that case, the traffic load from the network into the gateways may be more than the satellite can pass to the mobile stations. Additionally, for mobile-originated calls, a problem may arise in the network with alarms that are triggered when call failures due to radio problems exceed a defined threshold. The network's operations and maintenance (O&M) system could thus be flooded with alarms which would contain no useful information.
There are no known prior art teachings of a solution to the aforementioned deficiency and shortcoming such as that disclosed herein.
In order to overcome the disadvantage of existing solutions, it would be advantageous to have a method of re-routing calls through a backup satellite gateway whenever a gateway fails. In addition, in the event of a satellite failure or degradation of the satellite radio link, the method would rapidly recognize the problem and forward calls to voice mail prior to call abandonment. The present invention provides such a method.